Page 620 - Small Animal Clinical Nutrition 5th Edition

642 Small Animal Clinical Nutrition

mature body weight (Miller et al, 1964).
Box 32-2. Red Coat Syndrome.
VetBooks.ir ments.The ability of an animal’s coat to regulate body temper-
The skin and coat significantly influence nutrient require-
ature and energy requirements in cold environments correlates
The quantity and type of melanin pigments synthesized by fol-
licular melanocytes and deposited in keratinocytes are the closely with hair length, thickness and density and with the
prime determinant of mammalian hair color. Hair or fur color is medullation of individual hair fibers. In general, coats com-
genetically controlled but can be affected by various extrinsic posed of long, fine, poorly medullated fibers are the most effi-
factors, including nutrition. The two melanin pigments, eume- cient for thermal insulation at low environmental temperatures
lanin and phaeomelanin, are synthesized from a common pre- and thus help modulate energy requirements. The skin also
cursor, dopaquinone, which is a product of tyrosine oxidation. influences water requirements by minimizing transepidermal
Reports from breeders and pet owners have identified some moisture loss. Loss of this normal barrier function as a result of
cats and dogs that have had their coat change from black to a fatty acid deficiency can increase a patient’s water requirement,
reddish-brown color or have had hair stripes become less
noticeable. Controlled studies in cats and dogs suggest that which is clinically manifested as polydipsia (Burr and Burr,
dietary deficiency of the amino acid tyrosine or its precursor 1929, 1930; Basnayake and Sinclair, 1956).
phenylalanine is a significant factor causing black hair to The hair cycle, and thus the coat, is influenced by the gener-
change to a reddish-brown color. When tyrosine is limiting, al state of health, genetics, photoperiod, ambient temperature,
there is insufficient dopaquinone for full expression of eume- hormones, nutrition and poorly understood intrinsic factors
lanin formation and the yellow to reddish-brown phaeomelanin (Scott et al, 2001; Scott, 1990). Box 32-1 provides more details.
is the predominant pigment observed. Dog breeds can be classified as having high, moderate and
Tyrosine has not been regarded as an essential amino acid low weights of hair. Longhaired breeds with relatively large
because phenylalanine is metabolized to tyrosine in all mam- body surface areas per body weight, such as Pomeranians, have
mals and can supply the total tyrosine needs. Tyrosine con- the largest relative amount of hair. Estimates indicate that as
tributes to the total aromatic amino acid (phenylalanine plus much as 30% of protein in food is needed to maintain daily hair
tyrosine) requirement and can spare about half the phenylala-
nine requirement.This appears to be a unique situation in which growth in small breeds with long coats (Stafforst, 1982; Mundt
the need for a dispensable amino acid to support maximal and Stafforst, 1987). On the other hand, larger dogs with short
melanin synthesis in cats and dogs is much greater than that coats may use less than 10% of food protein to maintain daily
required for nitrogen balance or maximal growth. Dietary hair growth (Stafforst, 1982; Mundt and Stafforst, 1987).
phenylalanine plus tyrosine levels greater than 2% dry matter or Whether dogs of similar body surface areas have different
addition of L-tyrosine to the food should provide optimal amino requirements for protein and other nutrients based solely on
acid levels for maximal melanin synthesis in cats and dogs. their type of coat is unknown, but of possible clinical signifi-
cance. For example, there may be differences in nutrient
The Bibliography for Box 32-2 can be found at requirements during peak hair growth for a Pomeranian vs. a
www.markmorris.org. Chihuahua or an Old English sheepdog vs. a German short-
haired pointer based on coat type alone.
The epidermis has a renewable cell population.Keratinocytes
oyster shell or dicalcium phosphate, 2) a source of EFA such as migrate from the mitotically active pool in the basal layer of the
corn oil, safflower oil or some other vegetable oil and 3) a mul- epidermis, through the spinous layer and granular layer, and
tivitamin-trace mineral supplement. Also, homemade cat foods finally into the superficial stratum corneum, followed by nor-
should be supplemented with taurine. The final risk factor for mal exfoliation. The normal canine epidermis has a very slow-
nutritionally related skin disease is oversupplementation using ly renewing cell population. Only 1.5% of epidermal basal cells
naturally occurring foods or commercial supplements. Vitamin undergo DNA replication at any point in time (Kwochka and
A toxicosis is associated with excessive use of liver as a supple- Rademakers, 1989; Kwochka, 1990, 1991). In dogs, it takes
ment. High levels of minerals such as calcium in commercial approximately 22 days for cells to migrate from the basal layer
supplements can interfere with absorption of essential trace ele- to, but not through, the stratum corneum.
ments such as zinc. The upper external root sheath of the hair follicle and seba-
ceous gland have essentially the same cell kinetic growth char-
The Skin as a Metabolic Organ acteristics as the surface epidermis (Kwochka and Rademakers,
The skin is the largest organ of the body and the anatomic and 1989; Kwochka, 1990, 1991). Conversely, the root matrix of
physiologic barrier between the animal and its environment. anagen hairs is one of the most rapidly renewing cell popula-
The skin protects against water loss and physical, chemical and tions of the body (Kwochka, 1990). In actively growing hair, up
microbiologic injuries while its sensory components perceive to 24% of cells are undergoing DNA replication.
heat, cold, pain, touch, pruritus and pressure (Scott et al, 2001).
In addition, the skin is contiguous with several internal organs Key Nutritional Factors
and may reflect internal pathologic processes. The subcutis, The key nutritional factors for foods and nutritional supple-
skin and hair of a newborn puppy represent 24% of its body ments and the recommended amounts and doses for dogs and
weight, which decreases in some breeds to only 12 to 14% of cats with nutrient deficiency dermatologic problems are sum-